scholarly journals Tailoring Charge Reactivity Using In-Cylinder Generated Reformate for Gasoline Compression Ignition Strategies

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
Isaac W. Ekoto ◽  
Benjamin M. Wolk ◽  
William F. Northrop ◽  
Nils Hansen ◽  
Kai Moshammer
Keyword(s):  
Performance Metrics ◽  
Engine Performance ◽  
Gas Temperature ◽  
Exhaust Temperature ◽  
Start Of Injection ◽  
Low Load ◽  
Main Period ◽  
Ignition Characteristics ◽  
Negative Valve Overlap ◽  
Valve Overlap

In-cylinder reforming of injected fuel during a negative valve overlap (NVO) recompression period can be used to optimize main-cycle combustion phasing for low-load low-temperature gasoline combustion (LTGC). The objective of this work is to examine the effects of reformate composition on main-cycle engine performance. An alternate-fire sequence was used to generate a common exhaust temperature and composition boundary condition for a cycle-of-interest, with performance metrics measured for these custom cycles. NVO reformate was also separately collected using a dump-valve apparatus and characterized by both gas chromatography (GC) and photoionization mass spectroscopy (PIMS). To facilitate gas sample analysis, sampling experiments were conducted using a five-component gasoline surrogate (iso-octane, n-heptane, ethanol, 1-hexene, and toluene) that matched the molecular composition, 50% boiling point, and ignition characteristics of the research gasoline. For the gasoline, it was found that an advance of the NVO start-of-injection (SOI) led to a corresponding advance in main-period combustion phasing as the combination of longer residence times and lower amounts of liquid spray piston impingement led to a greater degree of fuel decomposition. The effect was more pronounced as the fraction of total fuel injected in the NVO period increased. Main-period combustion phasing was also found to advance as the main-period fueling decreased. Slower kinetics for leaner mixtures were offset by a combination of increased bulk-gas temperature from higher charge specific heat ratios and increased fuel reactivity due to higher charge reformate fractions.

scholarly journals Tailoring Charge Reactivity Using In-Cylinder Generated Reformate for Gasoline Compression Ignition Strategies

2016 ◽  
Author(s):  
Isaac W. Ekoto ◽  
Benjamin M. Wolk ◽  
William F. Northrop ◽  
Nils Hansen ◽  
Kai Moshammer
Keyword(s):  
Performance Metrics ◽  
Engine Performance ◽  
Combustion Stability ◽  
Gas Temperature ◽  
Exhaust Temperature ◽  
Start Of Injection ◽  
Main Period ◽  
Piston Crevice ◽  
Ignition Characteristics ◽  
Negative Valve Overlap

In-cylinder reforming of injected fuel during an auxiliary negative valve overlap (NVO) period can be used to optimize main-cycle combustion phasing for low-load Low-Temperature Gasoline Combustion, where highly dilute mixtures can lead to poor combustion stability. The objective of this work is to examine the effects of reformate composition on main-cycle engine performance for a research gasoline. A custom alternate-fire sequence with nine pre-conditioning cycles was used to generate a common exhaust temperature and composition boundary condition for a cycle-of-interest. Performance metrics such as main-period combustion stability and total cycle efficiency were collected for these custom cycles. The NVO-produced reformate stream was also separately collected using a dump valve apparatus and characterized in detail using both gas chromatography and photoionization mass spectroscopy. To facilitate gas sample analysis, sampling experiments were conducted using a five-component gasoline surrogate (iso-octane, n-heptane, ethanol, 1-hexene, and toluene) that matched the molecular composition, 50% boiling point, and ignition characteristics of the research gasoline. For the gasoline, it was found that the most advanced NVO start-of-injection (SOI) led to the most advanced main-cycle 10% burn angle. The effect was more pronounced as the fraction of total fuel injected in the NVO period increased. With the most retarded NVO SOI, shorter residence times and piston spray impingement limited the opportunity for injected fuel decomposition. For the gasoline surrogate, the most advanced NVO SOI had reduced reactivity relative to more intermediate NVO SOI, which was attributed to rapid in-cylinder mixing that led to a large amount of fuel quench in the piston crevice. For all NVO periods, combustion phasing advanced as the main-period fueling decreased. Slower kinetics for leaner mixtures were offset by a combination of increased bulk-gas temperature from higher charge specific heat ratios and increased fuel reactivity due to higher charge reformate fractions.

The Low Load Limit of Gasoline Partially Premixed Combustion Using Negative Valve Overlap

2012 ◽  
Author(s):  
Patrick Borgqvist ◽  
Öivind Andersson ◽  
Per Tunestål ◽  
Bengt Johansson
Keyword(s):  
Engine Speed ◽  
Premixed Combustion ◽  
Partially Premixed Combustion ◽  
Operating Region ◽  
Load Limit ◽  
Low Load ◽  
Negative Valve Overlap ◽  
Valve Overlap ◽  
Injection Strategies ◽  
High Octane

Partially premixed combustion has the potential of high efficiency and simultaneous low soot and NOx emissions. Running the engine in PPC mode with high octane number fuels has the advantage of a longer premix period of fuel and air which reduces soot emissions, even at higher loads. The problem is the ignitability at low load and idle operating conditions. The objective is to investigate different multiple-injection strategies in order to further expand the low load limit and reduce the dependency on negative valve overlap in order to increase efficiency. The question is, what is the minimum attainable load for a given setting of negative valve overlap and fuel injection strategy. The experimental engine is a light duty diesel engine equipped with a fully flexible valve train system. The engine is run without boost at engine speed 800 rpm. The fuel is 87 RON gasoline. A turbocharger is typically used to increase the boost pressure, but at low engine speed and load the available boost is expected to be limited. The in-cylinder pressure and temperature around top-dead-center will then be too low to ignite high octane number fuels. A negative valve overlap can be used to extend the low engine speed and load operating region. But one of the problems with negative valve overlap is the decrease in gas-exchange efficiency due to heat-losses from recompression of the residual gases. Also, the potential temperature increase from the trapped hot residual gases is limited at low load due to the low exhaust gas temperature. In order to expand the low load operating region further, more advanced injection strategies are investigated.

An Experimental Research on the Effects of Negative Valve Overlap on Performance and Operating Range in a Homogeneous Charge Compression Ignition Engine With RON40 and RON60 Fuels

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Seyfi Polat ◽  
Hamit Solmaz ◽  
Ahmet Uyumaz ◽  
Alper Calam ◽  
Emre Yılmaz ◽  
...  
Keyword(s):  
Pressure Rise ◽  
Engine Performance ◽  
Maximum Pressure ◽  
Compression Ignition ◽  
Compression Ignition Engine ◽  
Operating Range ◽  
Hcci Combustion ◽  
Residual Gas ◽  
Negative Valve Overlap ◽  
Valve Overlap

Abstract In this study, the effects of negative valve overlap (NVO) on homogenous charge compression ignition (HCCI) combustion and engine performance were experimentally investigated. A four stroke, single cylinder, port injection HCCI engine was operated at −16 deg crank angle (CA), −8 deg CA, and +8 deg CA valve overlap values and different lambda values and engine speeds at wide open throttle. RON40 and RON60 were used as test fuels in view of combustion and performance characteristics in HCCI mode. The variations of indicated mean effective pressure (IMEP), residual gas, CA50, indicated thermal efficiency (ITE), indicated specific fuel consumption (ISFC), maximum pressure rise rate (MPRR) and ringing intensity (RI) were observed on HCCI combustion. The results showed that NVO caused to trap residual gases in the combustion chamber. Hot residual gases showed heating and dilution effect on HCCI combustion. Combustion was retarded with the presence of residual gas at −16 deg CA NVO. Test results showed that higher imep and maximum in-cylinder pressure were obtained with RON60 according to RON40. As expected, CA50 was obtained later with RON60 compared to RON40 due to more resistance of auto-ignition. RON60 residual gas prevented the rapid and sudden combustion due to higher heat capacity of charge mixture. RI decreased with the usage of RON60 compared to RON40. Significant decrease was seen on RI with RON60 especially at lower lambda values. It was seen that HCCI combustion can be controlled with NVO and operating range of HCCI engines can be extended.

scholarly journals Cycle-by-cycle variations in autonomous and spark assisted homogeneous charge compression ignition combustion of stoichiometric air–fuel mixture

2018 ◽  
Vol 10 (3) ◽  
pp. 231-243 ◽  
Author(s):  
Jacek Hunicz
Keyword(s):  
Homogeneous Charge Compression Ignition ◽  
Fuel Injection ◽  
Fuel Mixture ◽  
Compression Ignition ◽  
Indicated Mean Effective Pressure ◽  
Start Of Injection ◽  
Negative Valve Overlap ◽  
Compression Ignition Combustion ◽  
Valve Overlap ◽  
Homogeneous Charge

This study investigates cycle-by-cycle variations in a gasoline fuelled, homogeneous charge compression ignition (HCCI) engine with internal exhaust gas recirculation. In order to study the effects of exhaust-fuel reactions occurring prior to the main combustion event fuel was injected directly into the cylinder at two selected timings during the negative valve overlap period. The engine was operated as both autonomous HCCI and spark assisted HCCI (SA-HCCI). The primary interest in this work was the operating region where the engine is switched between HCCI and spark ignition modes, thus operation with stoichiometric air–fuel mixture, which is typical for this region, was considered. Cycle-by-cycle variations in both combustion timing and indicated mean effective pressure (IMEP) were investigated. It was found that long-period oscillations of the IMEP occur when fuel injection is started at early stages of the negative valve overlap period, and that these can be suppressed by delaying the start of injection. This behaviour remained even when fuel injection was split into early and late-negative valve overlap injections. Spark assisted operation allowed eliminating late combustion cycles, thus improving thermal efficiency. However, characteristic patterns of IMEP variations were found to be the same for both HCCI and SA-HCCI operations, irrespective of the adopted negative valve overlap fuel injection strategy, as evidenced by using symbol-sequence statistics.

Internal exhaust gas recirculation via reinduction and negative valve overlap for fuel-efficient aftertreatment thermal management at curb idle in a diesel engine

2021 ◽  
pp. 146808742098459
Author(s):  
Mrunal C Joshi ◽  
Gregory M Shaver ◽  
Kalen Vos ◽  
James McCarthy ◽  
Lisa Farrell
Keyword(s):  
Diesel Engine ◽  
Fuel Consumption ◽  
Thermal Management ◽  
Lower Fuel Consumption ◽  
Low Load ◽  
Negative Valve Overlap ◽  
Valve Overlap ◽  
Gas Recirculation ◽  
Cycle Efficiency ◽  
Management Operation

Low air-flow diesel engine strategies are advantageous during low load operation to maintain temperatures of a warmed-up aftertreatment system (ATS) while reducing fuel consumption and engine-out emissions. This paper presents results at curb idle for internal EGR (iEGR) that demonstrate low airflow and reduced engine-out emissions during fuel-efficient ATS temperature maintenance operation. Internal EGR via reinduction and trapping using negative valve overlap (NVO) are compared to each other, conventional operation and to other low airflow approaches including cylinder deactivation (CDA). At 800 RPM/1.3 bar BMEP (curb idle) iEGR via reinduction enables 200°C engine-out temperature combined with 70% lower NO X, 35% lower fuel consumption, and 40% lower exhaust flow rate than conventional thermal management operation. Internal EGR via trapping using NVO resulted in an engine-out temperature of 185°C, with 56% lower NO X and 25% lower fuel consumption than conventional thermal management operation. Both iEGR strategies have lower engine-out temperatures and higher exhaust flow rates than CDA. No external EGR is required for either iEGR strategy. “iEGR via reinduction” outperforms “iEGR via NVO” as a result of higher open cycle efficiency (via less pumping work) and higher closed-cycle efficiency (via higher specific heat ratio).

Low-load expander deactivation studies for a light-duty single-shaft piston-compounded engine

2019 ◽  
pp. 146808741988650
Author(s):  
Peter Andruskiewicz ◽  
Russell Durrett ◽  
Paul Najt
Keyword(s):  
Gas Temperature ◽  
Exhaust Temperature ◽  
Positive Displacement ◽  
Current State ◽  
Light Duty ◽  
Trade Offs ◽  
Engine Design ◽  
Low Load ◽  
Optimum Solution ◽  
Exhaust Gas Temperature

A single-shaft, piston-compounded engine has shown great potential for improvements in efficiency over current state-of-the-art light-duty engines through the use of an efficient second expansion process to more fully recover energy still present in the exhaust gasses. This process inherently works well at mid to high loads where the displacement ratio of the piston expander can be maximized and fully utilized, but the positive-displacement nature of piston compounding creates a liability in efficiency and exhaust gas temperature at low loads. This study examined the trade-offs in efficiency, exhaust temperature, and engine design for various methods of mitigating the low-load deficiencies of the piston-compounded design. An optimum solution was identified, and these results were then used to guide the design of an experimental piston-compounded engine.

The Low Load Limit of Gasoline Partially Premixed Combustion Using Negative Valve Overlap

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Patrick Borgqvist ◽  
Öivind Andersson ◽  
Per Tunestål ◽  
Bengt Johansson
Keyword(s):  
Engine Speed ◽  
Premixed Combustion ◽  
Partially Premixed Combustion ◽  
Operating Region ◽  
Load Limit ◽  
Low Load ◽  
Partially Premixed ◽  
Negative Valve Overlap ◽  
Valve Overlap ◽  
Injection Strategies

Partially premixed combustion has the potential of high efficiency and simultaneous low soot and NOx emissions. Running the engine in partially premixed combustion mode with high octane number fuels has the advantage of a longer premix period of fuel and air which reduces soot emissions, even at higher loads. The problem is the ignitability at low load and idle operating conditions. The objective is to investigate different multiple-injection strategies in order to further expand the low load limit and reduce the dependency on negative valve overlap in order to increase efficiency. The question is, what is the minimum attainable load for a given setting of negative valve overlap and fuel injection strategy. The experimental engine is a light duty diesel engine equipped with a fully flexible valve train system. The engine is run without boost at engine speed 800 rpm. The fuel is 87 RON gasoline. A turbocharger is typically used to increase the boost pressure, but at low engine speed and load the available boost is expected to be limited. The in-cylinder pressure and temperature around top-dead-center will then be too low to ignite high octane number fuels. A negative valve overlap can be used to extend the low engine speed and load operating region. But one of the problems with negative valve overlap is the decrease in gas-exchange efficiency due to heat-losses from recompression of the residual gases. Also, the potential temperature increase from the trapped hot residual gases is limited at low load due to the low exhaust gas temperature. In order to expand the low load operating region further, more advanced injection strategies are investigated.

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